Sources, transport, and fate of arsenic in ground water

本研究的主要目标是表征新罕布什尔州已知含有高水平砷的地下水系统中砷的来源、运输和归宿。我们将通过研究新罕布什尔州内的四个地理区域中的每一个来实现这一目标，我们在作为试点项目完成的区域调查中确定了高砷水平。这将包括砷可能来自地质或人类来源的地区。在我们最近的研究中（Peters等人，1999）我们测量了从新罕布什尔州随机选择的家庭中收集的992个饮用水样品中的砷浓度。在钻探的基岩威尔斯井中发现砷含量很高，其中约35%的威尔斯井超过2克/升，这是美国环保局考虑的新的最高污染物水平标准的最低值。我们确定了四个砷含量高的地理区域，所有这些区域都在该州的南半部。最大的集群（弓，NH）进行了更详细的研究，发现有很高的砷在基岩，这是在一个容易浸出的形式。在这里提出的研究中，我们希望仔细调查四个集群中的每一个关于地下水系统的水文和地球化学。我们将使用1）基本水文技术绘制区域地下水流动模式，2）电子微探针x射线测绘以确定岩石和土壤中的砷载体相，3）柱实验以测量砷从基岩和土壤中溶解的化学条件，4）对沃茨进行物种特异性化学分析，以详细描述地下水系统的氧化还原条件和砷流动性的化学机制，（5）测定基岩和土壤延迟特性的柱试验。为了说明我们的方法，这项研究，我们将集中在两个领域的网站，我们已经做了一些初步的工作，这可能代表地质衍生与人类衍生的砷源的最终成员的情况下，在本建议书。这项工作的结果将进一步提高我们对含水层和矿山废物区中砷的来源和化学性质的一般认识。我们的研究将集中在一个以前强调不足的砷污染问题，在晶体（即，花岗质）地质阶地。我们的工作将提供信息，这将有助于在新英格兰和其他地方的砷污染结晶基岩地区的管理和补救方面做出更明智的决定。

The main goal of this study is to characterize the sources, transport and fate of arsenic in groundwater systems in New Hampshire which are known to contain high levels of arsenic. We will accomplish this goal by studying each of the four geographic regions within New Hampshire where high arsenic levels were identified by us in a regional survey that was completed as a pilot project. This will include regions where arsenic may be derived from either geologic or human-derived sources. In our recent study (Peters et al., 1999) we measured arsenic concentrations in 992 drinking water samples collected from randomly selected households in New Hampshire. Arsenic was found to be highly elevated in drilled bedrock wells, with approximately 35% of these wells exceeding 2 g/L, which is the lowest value being considered by the USEPA for the new maximum contaminant level standard. We identified four geographic regions with high arsenic levels, all of which are in the southern half of the state. The largest cluster (Bow, NH) was studied in more detail and found to have highly elevated arsenic in bedrock, which was in an easily leachable form. In the study proposed here, we wish to closely investigate each of the four clusters with respect to the hydrology and geochemistry of the groundwater systems. We will use 1) basic hydrologic techniques to map the regional groundwater flow patterns, 2) electron microprobe x- ray mapping to determine arsenic carrier phases in rocks and soils, 3) column experiments to measure the chemical conditions under which arsenic is solubilized from the bedrock and soils, 4) species-specific chemical analyses of waters to characterize in detail the redox conditions of the groundwater system and the chemical mechanisms responsible for arsenic mobility, and 5) column experiments to measure the retardatioin properties of bedrock and soils. For the purposes of illustrating our approach to this study, we will focus in this proposal on two field sites where we have done some preliminary work and which may represent the end-member cases of geologically-derived versus human-derived arsenic sources. Results from this work will further our general knowledge of the sources and chemistry of arsenic in the aquifers and mine waste areas. Our study will concentrate on a previously under-emphasized arsenic contamination problem in crystalline (i.e., granitic) geological teranes. Our work will provide information that will aid in making more informed decisions with respect to the management and remediation of arsenic- contaminated crystalline bedrock regions in new England and elsewhere.